I. Technical Field
The present invention concerns a light guide element for a lighting device, wherein the light guide element is elongated in the direction of a main axis and has a light entrance surface extending transversely relative to the longitudinal direction and a light exit surface emitting light transversely with respect to the longitudinal direction, and has two or more mutually superposed light guides.
II. Description of the Related Art
An example of a such light guide element is shown in DE 20 2007 003 497 U1 .
A disadvantage with that light guide element and other light guide elements known from the state of the art is that the light issues non-homogeneously from the light guide element, wherein it is not possible to implement a precise limit between a light region which is lit up and a dark region which is not lit up, this applying in particular to luminous density distribution, in spite of all endeavours, so that a vehicle headlight provided with such a light guide element inevitably blinds oncoming vehicle drivers.
In that respect blinding people who are looking in the direction of lighting devices is a great problem in various everyday regions of life. Besides the blinding effect which occurs in road traffic, that problem equally concerns street lighting arrangements, for example for lighting up tunnels, lighting public areas such as for example sports grounds, lighting workplaces or residences and so forth. Thus, for example, the risk of a fatal traffic accident is more than twice as high at night as in the day, although on average only a quarter of all accidents occur at night. In that respect a main reason for such blinding effects which are unpleasant in everyday life and dangerous in road traffic represents a light/dark limit of the lighting region of the lighting devices, that limit being defined exclusively by way of the intensity of lighting. It will be noted that what is more relevant for the blinding effect is the physiological lightness effect, afforded by the luminous density, which is specified in the units of candelas per square meter.
To make that light/dark limit sharper and more precise, the state of the art already discloses many different possible ways of bundling the light issuing from the light exit surface of headlights. Besides the methods which have already long been known of bundling by reflectors or mirrors, in recent times the light from one or more light sources is additionally bundled by means of a light guide element of a special configuration, wherein the light of the light sources is coupled into the light guide element in a light coupling-in region and is then passed for example by means of refraction and/or total reflection to a light exit surface where it thereupon illuminates a certain light region. For vehicle headlights that affords a light lobe which is generally shaped asymmetrically for low ray headlights.